Magnetic resonance imaging (MRI) is a medical diagnostic imaging technique used to diagnose many types of injuries and medical conditions. An MRI system includes a main magnet for generating a main magnetic field through an examination region. The main magnet is arranged such that its geometry defines the examination region. The main magnetic field causes the magnetic moments of a small majority of the various nuclei within the body to be aligned in a parallel or anti-parallel arrangement. The aligned magnetic moments rotate around the equilibrium axis with a frequency that is characteristic for the nuclei to be imaged. An external radiofrequency (RF) field applied by other hardware within the MRI system perturbs the magnetization from its equilibrium state. Upon termination of the application of the RF pulse, the magnetization relaxes to its initial state. During relaxation the time varying magnetic moment induces a detectable time varying voltage in the receive coil. The time varying voltage can be detected by the receive mode of the transmit coil itself, or by an independent receive only coil. An image processor then reconstructs an image representation from the received magnetic resonance signals for display on a human readable display.
MRI systems are made of many hardware components that work in conjunction with specialized software to produce the final images. FIG. 1 illustrates a MRI system of Prior Art, with the front cover removed so the main hardware components can be seen. Magnet 12 is the main hardware component of MRI system 10 and is responsible for producing the uniform main magnetic field, B0. Magnets used in MRI systems are very large and can have a horizontal or a vertical magnetic field.
Patient table 14, commonly called the patient couch, extends into bore 16 of magnet 12, and exists to support and position patient 18 so patient 18 can lie comfortably during the imaging process. Couch 14 houses mechanical as well as electrical components that allow patient 18 and couch 14 to be moved to the center of the magnet bore 16, to a point called isocenter 20, where the most uniform and sensitive area of magnet 12 is located and imaging commonly occurs.
Within the volume defined by main magnet is at least one gradient coil 22. Gradient coil 22 produces substantially linear spatially varying magnetic fields within the main magnetic field that are coincidental with the direction of the main magnetic field but vary along the three orthogonal directions (x, y, z) of the Cartesian coordinate system. Radiofrequency (RF) transmit coil 24 produces a perturbing RF pulses across the examination region.
One or more RF receive coils 26, commonly called imaging coils, are typically placed within the vicinity of the patient during imaging. RF receive coil 26 detects the time varying voltages induced by the magnetic moments during the relaxation time. There are many types of RF receive coils. Volume coils are placed around the anatomy of interest of the patient, and surface coils can be placed adjacent to the anatomy of interest of the patient. Internal coils also exist, designed to image the anatomy around the outside of the coil after the coil is inserted into the patient's body. RF receive coils are commonly designed for a specific anatomy of the patient's body, for example there are coils designed to image the knee, another to image the torso, and yet another for the head. In some systems RF receive coils can also be utilized as the RF transmit coil.
Along with the type of RF receive coil used, various patient data such as the size, position, and geometry of the patient, as well as that of the anatomy of interest and any motion within those areas also affects the optimization or selection of the RF coil system. The optimal coil is selected for the specific application. The technologist also chooses the proper positioning of the coil in relation to the imaging system and the proper positioning of the patient in relation to the coil for optimal images of the anatomy of interest. It is often a time-consuming process for the technologist to choose and set up the proper RF receive coil, position the patient correctly within the coil, and position the coil and patient properly within the imaging system.
There is a need within the art for an RF receive coil system that requires minimal positioning time by the technologist for increased throughput of patients during imaging sessions. One possible solution is an RF receive coil system that can easily be configured to optimally image patients of drastically varying sizes and shapes. Another useful attribute is an RF receive coil system that is capable of imaging the entire length of a patient's body without requiring re-positioning of the patient by the technologist. A further useful attribute is an RF receive coil system that does not touch or weigh down the patient.
Current commercially available RF receive coil systems accomplish whole body coverage by covering the patient in a multi-piece coil design. The whole body coil is split into numerous sections for ease of handling by the technologist. The technologist positions the patient on the table, places the a section over the patient's head and neck, another over their upper torso and an additional section over their lower torso. The patient table is then centered at isocenter over the anatomy of interest and imaging occurs. The patient table can be later moved again for imaging at further locations of the patient's body without repositioning of the patient within the coil. While the commercially available technology satisfies the desire for full-body coverage of the RF receive coil, it raises claustrophobia concerns, as it fully encompasses the patient's body at close proximity.